1. Technical Field
The present invention relates in general to a fuel additive that is a combustion catalyst for solid fossil fuel and in particular to a catalyst containing an over-based magnesium compound combined with a soluble iron compound. Such catalyst is particularly useful in heaters using coal or synfuel.
2. Description of the Prior Art
Concerns for the environment have led to more stringent restrictions on emissions from combustion of hydrocarbons, particularly from coal-burning equipment. Many techniques have been explored to reduce particulate emission, such techniques having various levels of success and various side effects. Typically, in the case of boilers, equipment design has been modified in order to minimize the emissions released. In addition to equipment design, various fuel sources have been evaluated for reduced emissions, including synfuel. Coal is also treated with various products to assist in dust control prior to combustion.
Emission controls additives have been researched in relation to liquid fuels. The use of fuel additives to reduce particulate emissions in liquid hydrocarbon combustion applications has been effective. In addition to tetraethyl lead for use in gasoline engines, several elements are known to have combustion catalyst characteristics useful for liquid hydrocarbon combustion chambers. Examples, are manganese, iron, copper, cerium, calcium and barium. Each of these elements has advantages and disadvantages in particular applications.
Other additives evaluated for use in liquid hydrocarbon have drawbacks including insolubility in hydrocarbons or lacking in the ability to create a dispersion in hydrocarbon liquid. Those additives that are water-soluble pose additional risks to the environment as spills or leaks from underground tanks could be hazardous to the environment.
In addition to iron, useful first row transition metals from the periodic table include manganese and copper. Also, various alkaline earth metals (barium, calcium) and others such as cerium, platinum and palladium have been tested. Manganese is used as a combustion catalyst in boilers with residual oil that often contains fuel contaminants, such as vanadium. Platinum and palladium, generally found in catalytic converters, are quite expensive. Manganese, when used alone, also forms low melting deposits and negates effects of magnesium on control of vanadium/sodium/calcium/potassium deposits. Iron catalyzes sulfur trioxide formation from sulfur dioxide increasing “cold end” corrosion (exhaust area) and sulfuric acid “rain” problems. Copper is less effective than either iron or manganese. Calcium forms tenacious deposits with other contaminant metals. Barium forms toxic salts. Cerium is not considered effective because of its higher elemental weight. These metals have been demonstrated to reduce smoke by no more than 50% at concentrations of up to about 50 PPM on a weight/weight basis by Environmental Protection Agency Test Method 5 (EPC M-5). While these metals have been evaluated in turbines and boilers, octane number is not at issue in this environment. Stability of the metal molecules is also not at issue and therefore not tested in boiler and turbines.
The effects of various metals listed above are known to improve combustion in boilers and combustion turbines and metals but these metals are known to vary ash quality. Tests run by this inventor indicate that improvement in emission controls can be achieved through the use of a mixture of magnesium and iron in a pre-selected ratio of about 5 parts magnesium to about 1 part by weight of iron. While some reduction in emissions from liquid hydrocarbon combustion was measured with this mixture, the reductions were low.
Over-based magnesium (Mg) compounds are known in the art for converting trace metal contaminants into high melting compounds and reducing deposits in combustion turbine engines operated by liquid petroleum fuels containing trace metal contaminants such as vanadium, lead, sodium, potassium and calcium. These contaminants form low melting corrosive deposits on hot metal parts in reciprocating engines, such as low-speed marine diesel engines. Magnesium is known to form high-melting salts with vanadium, sodium and other fuel contaminants. As a result, over-based magnesium compounds are used alone as fuel additives for compression-ignited reciprocating engines to reduce the effects of these contaminants.
A fuel additive for solid fossil fuel, such as coal, that includes a combustion catalyst to reduce smoke and particulate emissions from equipment that bums solid fossil fuels would be advantageous. A dispersible iron additive that remains stable during the combustion process would also be advantageous.